Council staff in Lisburn will take part in a second day of industrial action on September 30.
They will join local government and school support workers in England and Wales in the strike action.
The announcement follows the strike on 10 July, which saw around a million public service workers walk out in an increasingly bitter dispute over pay.
The union is calling on the Local Government Association to engage in further talks to resolve this year’s pay dispute. The current offer would see 90% of local government and school support workers receive a mere 1% increase, on the back of three successive years of pay freezes and below inflation rises in 2013 and 2014.
Pay has declined by 18% since 2010 and most councils have also imposed severe cuts on conditions such as unsocial hours payments.
Brian Ferguson, UNISON Regional Organiser for Northern Ireland said: “No local government or school support worker should be paid below the Living Wage.
“It’s time for the employers to come back to the negotiating table and work with us to secure a decent offer for our members and end this damaging dispute.”